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Cell Biology and Biochemistry > 5 - Mitochondria and Oxidative Phosphorylation > Flashcards

5 - Mitochondria and Oxidative Phosphorylation Flashcards

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1
Q

What is the theory of endosymbiosis? and why does this explain mitochondria having their own DNA

A
  • Ancestral eukaryotic cell engulfed an aerobic bacterium (mitochondria) by endocytosis
  • The cell could provide the bacterium with resources and the bacterium could provide the cell energy from oxygen
  • forming a symbiotic relationship
  • As a result mitochondria have their own genome and biosynthetic machinery for making RNA and Proteins
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2
Q

Describe the mitochondrial genome

A
  • Singular circular chromosome
  • Located in the matrix
  • 37 genes in total: 2 rRNA, 22tRNA, 13 protein encoding
  • very small compared to nuclear genome
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3
Q

what happens to male mitochondrial DNA?

A
  • It is degraded as soon as the sperm fertilises the egg, so we only have maternal Mitochondrial DNA
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4
Q

Talk about mitochondrial fission and fusion

A
  • Mitochondria are constantly fusing and dividing

- if for example 2 mitochondria fuse, then 1 large mitochondria will have 3 copies of mtDNA

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5
Q

how does mtDNA replicate

A
  • randomly

- just before fission mtDNA localise to mitochondrial polarities, to ensure they are incorporated into the new one

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6
Q

definition of Mitochondrial Biogenesis

A

the increase in abundance of mt proteins, mtDNA and mitochondrial numbers

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7
Q

when does mitochondrial biogenesis occur

A

when cells are stressed and need to produce more ATP

- eg during exercise

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8
Q

Describe the mitochondrial ribosome and the link to the mitochondrial genome

A
  • There are 2 rRNA genes in the mitochnodrial genome
  • rRNA form the subunits of ribosomes
  • Large 39s subunit made of 50 proteins
  • Small 28s subunit made of 30 proteins
  • Overall 55s and 80 proteins
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9
Q

what does s indicate

A
  • how fast they fall in a tube of suspension
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10
Q

55s mitochondrial ribosomes synthesise proteins coded by mtDNA, but mitochondria need more proteins than they can make to survive, where do these proteins come from

A
  • cytosolic/cytoplasmic Ribosomes
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11
Q

is the inner mitochondrial membrane very permeable or impermeable

A
  • inner is very impermeable

- outer is more permeable

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12
Q

Describe how precursor proteins in the cytoplasm enter the mitochondrial matrix

A
  • chaperone proteins bind to the precursor protein and prevent it from folding so it can be pulled into the matrix
  • The special signal sequence on the precursor protein binds to a receptor protein in TOM complex on outer mt membrane
  • TOM pulls the protein across the outer membrane into the intermembrane space
  • The special signal sequence then binds to TIM 23 complex which translocates the precursor protein across the inner membrane
  • the chaperone protein is then lost and the special signal sequence cleaved leaving the protein to fold
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13
Q

what enzyme cuts off the special signal sequence from the precursor protein

A
  • signal peptidase
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14
Q

What do TOM and TIM stands for and where are they located

A

TOM - Translocase Outer-Membrane complex

Tim - Translocase Inner Membrane complex

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15
Q

What is a special signal sequence

A
  • a specific series of amino acids recognised by a specific receptor
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16
Q

How does Pyruvate transport into the mitochondrial matrix from the cytoplasm

A
  • Pyruvate is small enough to travel through porins in the outer mitochondrial membrane
  • Pyruvate then travels from the intermembrane space into the matrix through Mitochondrial Pyruvate Carriers
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17
Q

what happens to pyruvate once its in the matrix

A
  • pyruvate is decarboxylated to form Acetyl CoA
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18
Q

How do Fatty acids transport into the Mitochondrial Matrix

A
  • Fatty acids cannot cross either mt membrane so have to be converted
    1) Fatty acid is combined with CoA forming fatty Acyl CoA in an unfavourable reaction costing 1 ATP
    2) fatty Acyl CoA is then combined with carnitine via the enzyme CPT1 located on the outer mt membrane, this forms Acyl-Carnitine
    3) Acyl-Carnitine can travel through porins through the outer mt membrane
    4) Acyl-Carnitine is then transported into the matrix through the protein translocase which is an antiporter which moves carnitine out of the matrix at the same time
19
Q

What happens to Acyl-Carnatine once it is in the matrix

A

Acyl-Carnitine in converted back into fatty Acyl CoA and carnitine by CPT 2, Carnitine is then shipped out of the matrix through the protein translocase antiporter

20
Q

Where are CPT1, CPT2, porins and protein translocase located?

A

CPT1 and Porins - Outer mitochondrial membrane

CPT 2 and Protein translocase - Inner mt membrane

21
Q

What do the proteins CPT1, CPT2, porins and protein translocase do or transport?

A

CPT1 : Combines fatty acyl CoA and Carnitine to produce Acyl-Carnitine
CPT2: Converts Acyl-Carnitine back into fatty acyl CoA and Carnitine
porins: Acyl Carnitine
protein translocase: Acyl carnitine

22
Q

How is NADH transported into the the mitochondria

A

The Malate-Aspartate shuttle

  • Oxaloacetate in the intermembrane space is reduced to malate through the oxidation of NADH
  • Malate can travel into the matrix through an antiporter protein with a-ketoglutarate
  • Malate is now oxidised into oxaloacetate again, which in return reduces NAD+ into an NADH
  • Oxaloacetate is transaminated into aspartate, while glutamate is converted into a-ketoglutarate
  • Aspartate can travel back into the intermembrane space through an antiporter when glutamate enters the matrix
  • Aspartate is then transaminated back into oxaloacetate and a-ketoglutarate is converted into glutamate
23
Q

what enzyme catalyses transamination of oxaloacetate and aspartate

A
  • transaminase
24
Q

where does the malate aspartate shuttle occur

A

across the inner mitochondrial membrane

25
Q

what enzyme catalyses the reduction and oxidation of malate and oxaloacetate thus reducing and oxidising NADH/NAD+

A

Malate dehydrogenase

26
Q

where is oxaloacetate reduced

A

when oxaloacetate is reduced, NADH is oxidised into NAD+, which reduces the amount NADH. we want more NADH in the matrix so this happens in the inter membrane space

27
Q

Name all the proteins we know on the inner mitochondrial membrane

A
  • TIM (Proteins transport)
  • Mitochondrial pyruvate carriers (pyruvate transport)
  • Acyl-Carnitine translocase (Fatty acid transport)
  • Antiporters in malate aspartate shuttle (NADH)
28
Q

Name all the proteins we know on the outer mitochondrial membrane:

A
  • TOM (protein transport)

- Porins (pyruvate and fatty acid transport)

29
Q

Name the complexes in the electron transport chain

A

1- NADH dehydrogenase
2- Succinate dehydrogenase
3- Cytochrome C reductase
3- Cytochrome C oxidase

30
Q

what are ubiquinone and cytochrome

A
  • mobile electron carriers
31
Q

give a summary of the electron transport chain

A
  • high energy electrons carries by NADH and FADH2 are passed into the electron transport chain and accepted by a series of electron carriers
  • The electrons lose their energy as they pass along the chain
  • the energy pumps H+ across the inner mitochondrial membrane to the intermembrane space
  • the electrons are passed to oxygen forming water
32
Q

Describe the structure of complex 1 in the ETC

A
  • FMN is the electron acceptor

- There is an iron-sulphur cluster that links FMN to ubiquinone (Q)

33
Q

Describe the process of what happens at Complex 1

A
  • NADH donates is electron to complex 1 (NADH dehydrogenase) and is oxidised to NAD+
  • FMN accepts the electron and passes the electron down the series of iron-sulphur clusters to ubiquinone
  • Ubiquinone (Q) accepts the electron forming QH2 or CoQH2, now having the energy from the electron
  • In passing the electrons down the iron sulphur clusters some electron energy some electron energy is lost and used to pump 4H+ across the inner mt membrane into the inter-membrane space
34
Q

What are the results of complex 1 NADH dehydrogenase

A
  • 4 H+ pumped into the inter-membrane space
  • an oxidised NADH or (NAD+)
  • ubiquinone with an electron (CoQH2 or QH2)
35
Q

Describe the process of what happens at complex 2 (succinate dehydrogenase) in the electron transport chain

A
  • At complex 2 succinate is oxidised into fumarate (step 6 of the TCA cycle)
  • At the same time FAD is reduced into FADH2
  • FADH2 instantly donates its electrons to complex 2
  • The electrons pass down a series of iron-sulphur clusters until reaching the final stop
  • at the final stop CoQ is reduced to CoQH2 by gaining 2 electrons and 2 H+
36
Q

what is the final result from complex 2 in the electron transport chain

A
  • Succinate is oxidised to fumarate
  • FAD is reduced to FADH2
  • CoQ is reduced to CoQH2
37
Q

describe the process of what happens at complex 3 (Cytochrome C reductase) in the electron transport chain

A
  • CoQH2 from complex 1 or 2 donates its 2 electrons to the iron-sulphur clusters in complex 3 becoming CoQ
  • The 2 H+ from oxidised CoQH2 are released into the intermembrane space
  • The electrons pass across the iron-sulphur clusters to cytochromes.
  • Cytochromes accept the electrons and pass each one to a cytochrome C mobile electron carrier
  • Enough energy is released by the electrons in the iron-sulphur clusters to pump 2 more H+ into the intermembrane space
38
Q

What is the result of Complex 3

A
  • CoQH2 is oxidised donating 2 electrons to complex 2 and also 2 H+ are released into the intermembrane space
  • 2 H+ are pumped into the intermembrane space
  • 2x Cytochrome C mobile electron carrier gains an electron and is reduced
39
Q

Describe the structure of complex 3

A
  • Contains a series of iron-sulphur clusters which lead to cytochrome
  • also has cytochrome C which are mobile electron carriers attached
40
Q

Describe the process of what happens at Complex 4 (Cytochrome C oxidase) in the electron transport chain

A
  • 4 cytochrome C mobile electron carriers arrive and donate their single electrons to complex 4
  • This has to be 2 electrons generated from 2 FADH2 (Complex 2) and 2 NADH (complex 1)
  • These electrons are passed to an O2 molecule and combines with 4H+ from the matrix to give 2 H20
  • This combination generates enough energy to pump 4 H+ from the matrix into the inter membrane space
41
Q

What is the result from complex 4 (Cytochrome C Oxidase) in the ETC?

A
  • 4H+ pumped into intermembrane space
  • 2 H2O generated
  • 4 Cytochrome C oxidised
42
Q

What are the 3 driving forces that result in oxidative phosphorylation

A
  • Large pH difference
  • Large concentration gradient
  • Large electrical charge difference
43
Q

Describe how ATP synthase uses the electrochemical proton gradient to generate ATP

A
  • Protons enter ATP synthase through the F0 region into the a subunit
  • Protons then move into the c subunit of the F0 region causing some rotation/mechanical energy
  • The protos leave into the matrix after driving around the c subuint
  • c is linked to the shaft which rotates very quickly
  • as the shaft rotates this causes a conformation change to alpha and beta subunits of F1 which catalyses the formation of ATP
44
Q

Describe the structure of ATP synthase

A
  • 2 regions F0 andF1
  • electrons enter and pass through F0
  • F1 is where ATP is generated
  • F0 contains subunits abc
  • F1 contains subunits alpha and beta

Cell Biology and Biochemistry (9 decks)

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